Permanently attached piezoelectric sensors arranged in a spatially distributed array are under consideration for structural health monitoring systems incorporating active ultrasonic methods. Most damage detection and localization methods that have been proposed are based upon comparing monitored signals to baselines recorded from the structure prior to initiation of damage. To be effective, this comparison process must take into account any conditions other than damage that have changed the ultrasonic signals. Proposed here is a two-step process whereby damage is first detected and is then localized and characterized. The detection strategy considers the long time behavior of the signals in the diffuse-like regime where distinct echoes can no longer be identified. The localization strategy is to generate images of damage based upon the early time regime when discrete echoes from boundary reflections and scattering sites are meaningful. Results are shown for an aluminum plate with artificial damage introduced in combination with temperature variations. The loss of local temporal coherence combined with an optimal baseline selection procedure is shown to be effective for the detection of damage, and a delay-and-sum imaging method applied to the residual signals both localizes the damage and provides characterization information.

http://iopscience.iop.org/article/10.1088/0964-1726/17/3/035035/pdf

Detection, localization and characterization of damage in plates with an in situ array of spatially distributed ultrasonic sensors

Efficient temperature compensation strategies for guided wave structural health monitoring

This article presents in a unified way, the various optimization criteria used by researchers for optimal placement of piezoelectric sensors and actuators on a smart structure. The article discusses optimal placement of piezoelectric sensors and actuators based upon six criteria: (i) maximizing modal forces/moments applied by piezoelectric actuators, (ii) maximizing deflection of the host structure, (iii) minimizing control effort/maximizing energy dissipated, (iv) maximizing degree of controllability, (v) maximizing degree of observability, and (vi) minimizing spill-over effects. Optimal piezoelectric sensor and actuator locations on beam and plate structures for each criterion and modes of interest are presented in a tabular form. This technical review has two objectives: (i) practicing engineers can pick the most suitable philosophy for their end application and (ii) researchers can come to know about potential gaps in this area.

Optimization Criteria for Optimal Placement of Piezoelectric Sensors and Actuators on a Smart Structure: A Technical Review

It is desirable for any structural health monitoring (SHM) system to have maximum sensitivity with minimum sensor density. The structural health monitoring system described here is based on the excitation and reception of guided waves using piezoelectric elements as sensors. One of the main challenges faced is that in all but the most simple structures the wave interactions become too complex for the time domain signals to be interpreted directly. One approach to overcoming this complexity is to subtract a baseline reference signal from the measured system when it is known to be defect free. This strategy enables changes in the structure to be identified. Two key issues must be addressed to allow this paradigm to become a reality. First, the system must be sufficiently sensitive to small reflections from defects such as cracking. Second, it must be able to distinguish between benign changes and those due to structural defects. In this paper the baseline subtraction approach is used to detect defects in a simple rectangular plate. The system is shown to work well in the short term, and good sensitivity to defects is demonstrated. The performance degrades over the medium to long term. The principal reason for this degradation is shown to be the effect of change in temperature of the system. These effects are quantified and strategies for overcoming them are discussed.

http://iopscience.iop.org/article/10.1088/0964-1726/15/4/010/pdf

The temperature stability of guided wave structural health monitoring systems

Active vibration control of smart piezoelectric beams: Comparison of classical and optimal feedback control strategies

In this paper, a comprehensive methodology for locating and determining the extent of linear cracks in homogeneous plates based on the time-of-flight analysis of Lamb wave propagation is proposed. Piezoelectric sensors and actuators (PZTs) placed on a square grid configuration are used to excite and receive direct and reflected waves. The actuation frequency, spacing of PZTs and length of the signal to analyze are first determined. The grid is used to sweep across the plate to identify the location of a crack, if there is one. Elliptical loci of possible crack positions are constructed based on the flight time of crack-reflected waves estimated using energy spectra from the Hilbert–Huang transform of the sensor signals. A detailed procedure for obtaining the ellipses is described, including the blind zones. After identifying the crack position, the crack orientation is determined by varying the positions of the PZTs and observing the strength of the energy peaks in the Hilbert spectra. This provides the basis for moving the PZTs to estimate the extent of the crack. Experimental results obtained using aluminum plates with through, half-through and concealed cracks showed that the proposed method is feasible and accurate.

https://iopscience.iop.org/article/10.1088/0964-1726/13/4/002/pdf

Detection of cracks in plates using piezo-actuated Lamb waves

This study on the vibration control of smart piezoelectric composite plates investigates the effect of the stretching-bending coupling of the piezoelectric sensor/actuator pairs on the system stability of smart composite plates. Based on first-order shear theory and consistent methodology, a smart isoparametric finite element is formulated and the classical negative velocity feedback control method is adopted for the active vibration control analysis of smart composite plates with bonded or embedded distributed piezoelectric sensors and actuators. It is shown mathematically and demonstrated numerically that generally the coupling effect tends to result in system instability unless the sensor/actuator pairs are collocated or the plate simply supported. The result of this study can be used to aid the placement of piezoelectric sensor/actuator pairs of smart composite plates as well as for robust controller design.

https://iopscience.iop.org/article/10.1088/0964-1726/10/4/306/pdf

Vibration control of smart piezoelectric composite plates

The propagation of Love waves in a piezoelectric lamina bonded onto a semi-infinite solid medium is investigated in this paper. The dispersive characteristics and the mode shapes of the deflection and the electric potential in the thickness direction of the piezoelectric layer are theoretically derived. Numerical simulations show that the phase velocities initiate at the shear wave velocity of the host medium and tend towards the Bleustein-Gulyayev surface wave velocity for the piezoelectric layer at high wavenumbers for the first mode. The first two mode shapes of the electric potential correspond to a half-cosine and a full-cycle sinusoidal distribution, respectively, and become distorted as the wavenumber increases. These findings are significant in the application of inter-digital transducers for surface wave excitation in structural health monitoring.

https://iopscience.iop.org/article/10.1088/0964-1726/10/2/325/pdf

Love waves in piezoelectric coupled solid media

A simple optimal placement strategy of piezoelectric sensor/actuator (S/A) pairs for vibration control of laminated composite plate is presented, where the active damping effect under a classical control framework is maximized using the finite element approach. The classical direct pattern search method is employed to obtain the local optimum, where two optimization performance indices based on modal and system controllability are studied. The start point for the pattern search is selected based on the maxima of integrated normal strains consistent with the size of the collocated piezoelectric patches used. This would maximize the virtual work done by the equivalent actuation forces along the strain field of an initial state. Numerical simulation using a cantilevered and a clamped composite square plate illustrate the effectiveness of the proposed strategy, where the results coincide with the global optimal layout from exhaustive search for both modal and system controllability indices. The number of tria...

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Papers

Detection of cracks in plates using piezo-actuated Lamb waves

Vibration control of smart piezoelectric composite plates

Love waves in piezoelectric coupled solid media

Vibration Control of Composite Plates via Optimal Placement of Piezoelectric Patches

Enhancing flutter and buckling capacity of column by piezoelectric layers